I. Technical Field of the Invention
This invention relates to a coated abrasive and more particularly to coated abrasives containing abrasive agglomerates made in situ through target cores with a preferred distribution. The abrasive particles are oriented with sharp edges all over the cores which create extended surfaces for improving the abrading capacity of the abrasive articles.
II. Description of the Background
Coated abrasives typically consist of a single layer of abrasive grain adhered to a backing. It has been found that not more than about 15% of the grains of abrasive are utilized in removing material from any workpiece. Thus, about 85% of the grains are wasted (U.S. Pat. No. 5,039,311 Bloecher et al.). To overcome this problem of waste the industry is continuously seeking to extend the life of coated abrasive products.
In efforts to extend the life of coated abrasive products, various studies have been made to achieve a distribution of the abrasive particles on the substrate so that the majority of particles are used. For example, U.S. Pat. No. 2,115,897 (Wooddell et al.) describes a coated abrasive article comprising a flexible band made of a plurality of blocks of bonded abrasive material attached to the band by a resin layer forming a pattern.
U.S. Pat. No. 2,242,877 (Albertson) describes the production of coated abrasives in the form of abrasive discs with different patterns produced with different layers of abrasive particles.
U.S. Pat. No. 2,755,607 (Haywood) describes the production of a coated abrasive with a uniform pattern of grooves or indentations in the abrasive surface. The pattern is provided by the deposition of an adhesive by a roller coating operation. The adhesive layer, while still wet or in a softened condition, is shaped into a series of parallel, narrow-width groove portions which alternate with a parallel series of land portions appreciably thicker than the groove portions without breaking the continuity of the adhesive layer.
U.S. Pat. No. 3,048,482 (Hurst) describes the manufacture of a novel type of abrasive article, comprising a flexible support of backing to which is affixed an abrading body made up of a multiplicity of individual small abrasive bodies. Each of these bodies is roughly pyramidal in shape and comprised of discrete abrasive granules. A rigid, heat-hardened, organic bond is produced using an adhesive selected from the group consisting of heat-hardened, phenolic resins and vulcanized hard rubbers.
U.S. Pat. No. 3,916,584 (Howard et al.) describes a spheroidal composite particle comprising about 6-65% by volume of fine abrasive grains having a Knoop hardness of at least about 1500 and an effective diameter on the order of 25 microns or less. In a preferred method of manufacture, the abrasive grains are dispersed in a metal oxide gel, the gel is dehydrated to leave spheroidal composite granules and the granules are heated to drive off remaining water.
U.S. Pat. No. 3,918,217 (Oliver) describes cutting and abrading devices made with special predetermined protrusions armed with metal bonded refractory metal grit. The abrading tool structure comprises a plurality of spherical steel shot particles forming protrusions and magnetically-oriented, abrasive grit particles. A metal bonding material holds the abrasive grit particles and steel shot particles in proper position. The ratio of protrusion to grain size should be 1 to 3. The deposition of abrasive could be in either a single layer or a pyramidal arrangement.
U.S. Pat. No. 3,928,949 (Wagner) describes a grinding material comprising a multiplicity of hollow bodies whose walls contain abrasive grains on more than 50% of the wall surface with a bonding means selected from the group consisting of synthetic resins. The diameter of the hollow bodies is between 0.1 and 8 mm and is not more than 50 times the mean grain diameter. The abrasive grains are contained substantially within the walls of the hollow bodies.
U.S. Pat. No. 4,132,533 (Löhmer et al.) describes a process for producing abrasives in the form of hollow spheres, wherein abrasive grains are anchored on a thermoplastic, spherical supporting surface by heating. The diameter of the thermoplastic, spherical supporting surface is from 0.5 to 6 mm, with abrasive grains from 63 to 150 microns in size.
U.S. Pat. No. 4,311,489 (Kressner) describes a coated abrasive product having a solid agglomerate of fine abrasive grains having an average diameter less than about 200 microns and an inorganic, brittle, cryolite matrix. The agglomerates have an irregular surface producing a strong bond to the matrix and size coats which permit gradual wearing down of the agglomerates during grinding by gradual removal of dulled abrasive grains from the agglomerates. The matrix bond serves to limit the depth of penetration into the workpiece of the individual abrasive grains during the grinding action and thereby provides a surface finish comparable to the surface finish utilizing unagglomerated abrasive grains of the grit size of the individual grains in the agglomerates.
U.S. Pat. No. 4,551,842 (Rostoker) describes abrasive agglomerate particles comprising a matrix of multi-cellular foamed glass with abrasive grit particles encapsulated within the cell walls of the glass. The agglomerates have a spherical shape. Unfortunately, the results of this invention show no reproducibility or consistency.
U.S. Pat. No. 4,652,275 (Bloecher et al.) describes an abrasive article comprising erodible agglomerates formed by a multiplicity of individual grains of abrasive mineral. The agglomerates contain about 60 to about 95 weight percent individual abrasive grains and about 0.3 to about 8 weight percent matrix material. The final size of the agglomerates was about 20 to about 100 microns.
U.S. Pat. No. 4,799,939 (Bloecher et al.) describes erodable agglomerates containing individual abrasive grains disposed in an erodable matrix comprising hollow bodies and a binder. The hollow bodies preferably comprise hollow microspherical particles formed from glass. The size of the agglomerates range from 150 to 3000 microns.
U.S. Pat. No. 5,039,311 (Bloecher) describes an erodable abrasive granule comprising an erodable base agglomerate formed by a plurality of first abrasive grains in a binder and a coating comprising a plurality of second abrasive grains bonded to at least a portion of the base agglomerate. The second abrasive grains are larger than the first abrasive grains.
U.S. Pat. No. 5,219,462 (Bruxvoort et al.) describes an abrasive article that has abrasive composite members secured firmly in recesses in a backing sheet in a precise pattern to produce a desired lateral spacing between each abrasive composite member. The composite members are produced through the back concentrated in patterns with grooves which are filled by means of an abrasive mixture including blowing agents in which heat increases its size and forms abrasive protrusions.
U.S. Pat. No. 5,437,754 (Calhoun) describes a method of forming an abrasive article comprising the steps of providing an embossed carrier web having a plurality of recesses formed in the front surface thereof and filling the recesses with an abrasive composite slurry having a plurality of abrasive grains dispersed in a hardenable precursor.
U.S. Pat. No. 5,578,098 (Gagliardi et al.) describes a coated abrasive article comprising a backing of erodible agglomerates and abrasive grains on at least one major surface thereof. The erodible agglomerates consist essentially of a grinding aid and the erodible agglomerates are in the form of rods. The agglomerates may also be dispersed between, above or both between and above the abrasive grains.
U.S. Pat. No. 5,681,217 (Hoopman et al.) describes an abrasive article comprising a sheet-like structure including a major surface extending within a first imaginary plane with a plurality of individual, three-dimensional abrasive composites dispersed in fixed positions thereto in an array. Each of these composites comprises abrasive particles dispersed in a binder. Each of these composites has a substantially precise shape characterized by a distal end extending farthest from the major surface, so that the composites comprise a geometrical shape having a first portion in contact with the major surface and a second portion as an outer end. The first portion comprises a frusto-conical shape, while the second portion comprises a rounded shape.
U.S. Pat. No. 5,928,394 (Stoetzel) describes an abrasive article containing an abrasive coating having more than one abrasive composite layer. Stoetzel also describes a method of manufacturing which forms a defined pattern such as a pyramid. Such a pattern is constructed of abrasive slurries deposited on one another to form the defined shape, where each abrasive slurry may contain different abrasive particles with the same or different size and different adhesives.
U.S. Pat. No. 5,928,394 (Christianson) describes a coated abrasive article comprising abrasive agglomerates in the shape of a truncated four-sided pyramid. Also described is a method of making the coated abrasive article consisting of making the agglomerate by molds and subsequently depositing them on a substrate to produce the coated abrasive.
U.S. Pat. No. 6,299,508 (Gagliardi) describes an abrasive article comprising a base layer having both a first surface and a second surface, and a plurality of protrusions comprising grinding aids integrally molded with the base layer. The first surface of the base layer is contoured by the protrusions to define a plurality of peaks and valleys. A coating of abrasive particles is adhered to the contoured first surface to cover at least a portion of both the peaks and the valleys.
U.S. Pat. No. 6,790,126 (Wood et al.) describes agglomerate abrasive grains comprising a plurality of abrasive particles bonded together with a sintered, crystalline, ceramic bonding material. The bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight crystalline Al2O3, based on the total metal oxide content of the bonding material. The abrasive particles have an average particle size of at least 5 micrometers.
U.S. Pat. No. 6,797,023 (Knapp et al.) describes coated abrasives comprising abrasive agglomerate grains characterized by a high porosity and low ratio of solid volume to nominal volume which provide an exceptionally useful medium for low pressure grinding characteristics. The method for obtained the agglomerate abrasive grains employs a rotary dryer which incorporates a partially agglomerated abrasive mixture of synthetic resins and inorganic fillers introduced to a rotary dryer. The temperature is raised above 500° C. to calcine all organic material so that the space occupied by this material serves as the abrasive agglomerate porosity and so that the inorganic filler melts and serves as a binding agent.
U.S. Pat. No. 7,410,413 (Woo et al.) describes a structured abrasive article comprising a backing having first and second opposed major surfaces and a structured abrasive layer having an outer boundary and affixed to the first major surface of the backing. The structured abrasive layer comprises a plurality of raised abrasive regions. Each raised abrasive region consists essentially of close-packed, pyramidal abrasive composites having a first height and a network consisting essentially of close-packed, truncated, pyramidal abrasive composites having a second height. The network continuously abuts and separates the raised abrasive regions from one another and is coextensive with the outer boundary.
U.S. Pat. Application Ser. No. 2009/0139149 A1 (Sachse) describes an abrasive grain with a core of melted spherical corundum characterized by the spherical corundum being coated with a layer of at least one binder and fine-grained, abrasive solid particles. The agglomerate size is a medium diameter ranging from 0.5 to 5 mm, while the size of the abrasive grains ranges from 50 to 500 microns. The agglomerate grain is used for bonded abrasives.
U.S. Pat. Application Ser. No. 2011/0056142 A1 (Sheridan) describes methods for forming aggregate, abrasive grains for use in the production of abrading or cutting tools. The method comprises providing abrasive core particles; coating these particles with an adhesive, the adhesive comprising a binding agent and a solvent for the binding agent; separately dropping the adhesive-coated core particles onto a layer of abrasive peripheral particles and covering the dropped core particles with further peripheral particles, in such way as to form aggregate particles, each of which comprises a core particle having peripheral particles attached to it; and consolidating the aggregate particles by causing the solvent to evaporate by letting the adhesive set.
U.S. Pat. Application Ser. No. 2013/0280995 A1 (Dopp et al.) describes an abrasive having a base body with abrasive particles applied to its surface wherein the base body has a multi-cellular structure. Glass is used for the multi-cellular base bodies.
As seen above, most of the approaches taken by the industry and by those skilled in the art to increase the life of the coated abrasive focus on obtaining a coated abrasive with abrasive agglomerates and/or defined patterns. The majority of these patents involve additional processes for manufacturing the agglomerated abrasive particles, using in most cases different machines and requiring high temperatures above 300° C. which involve high energy costs and an excessive number of process steps.
While pattern formation in most of these prior methods involves abrasive slurries, the coated abrasives produced by these methods do not produce abrasive with defined grain orientation for the abrading process. New edges are randomly distributed into the agglomerate together with the resin binders and fillers.
In most of the methods described in the above patents, parts of the agglomerates are flooded by the resin binders in order to affix them to the selected backing. These abrasive portions do not work and are considered as a foundation base to avoid shelling during the sanding process. These portions may also be considered as wasted materials, because no abrasive benefits are obtained from them.
Thus, there has been a long-felt, but unfulfilled need for improved, coated abrasive materials and for methods of producing such materials without requiring additional process stops and equipment. Further, there has been a continuing need for coated abrasive materials where the abrasive particles are oriented to produce consistent abrasion and extended useful life during the abrading process.